Optimization Of Method For Determining Antimony Stable Isotopes And Its Preliminary Application

In recent years,with the application and promotion of the Multiple-Collector Inductively Coupled Plasma Mass Spectrometer(MC-ICP-MS),the research on non-traditional stable isotopes has made rapid development.As a redox sensitive element,antimony(Sb)has great potential for its isotope to trace the source,migration,transformation,and return of antimony in the environment,as well as the inversion of paleo-ocean redox conditions.However,the antimony isotope standard solution has not yet been unified internationally,and the establishment of a universal antimony isotope analysis method is relatively lagging.There are few systematic reports on the antimony isotope composition of comparable geological standard samples.At present,the data of different antimony reservoirs are in the accumulation stage.These problems not only hinder the research of antimony isotope,but also restrict the development and application of antimony isotope theory.Based on the above problems and previous studies,this article optimized a universal Sb isotope analysis method through a series of conditional experiments,and reported the Sb isotope composition of common geological standard samples,and studied the antimony in the weathering section of Shadi.The law of isotope variation and the influencing factors of antimony isotope fractionation in the profile were discussed,and the following points of understanding were obtained:(1)Sb isotope separation and purification method is divided into two steps.The first step uses cationic resin AG50W-X8 to remove K,Ca,Fe,Zn and other matrix elements in the sample.In the second step,a new type of silicon-based mercapto resin is used to remove elements such as As,Ge,Se,Sn,Te,and retain the target element Sb.After the sample was purified,Sn/Sb<0.001 and Te/Sb<0.0001,which realized the separation of Sb from the main interfering elements Sn and Te.The blank of the whole process is 0.3-0.5ng,and the recovery rate of Sb is stable above 95%.The optimized method is simple to operate and is suitable for Sb separation and purification of most geological and environmental samples.(2)Using the hydride generation system(HG)made by the research group in conjunction with MC-ICP-MS,using Cd as the external standard element(ED),combined with the standard-sample matching method(SSB).The Sb isotope ratios of common geological standard samples were tested,and we evaluated the reliability of Sb isotope analysis method.The long-term test results of the international standards NIST SRM 3102a and Alfa Sb are0.00±0.06‰(2SD,N=66)and 0.22±0.06‰(2SD,N=23),respectively.Based on the NIST SRM3102a standard solution,we report the Sb isotopic composition of 24 common geological and environmental standard samples.The sample types involve magmatic rocks,sedimentary rocks,iron-manganese nodules,cobalt-rich crusts,soil samples,river sediments and plants.River sediments GSD-3(0.46±0.09‰,2SD),GSD-10(0.42±0.12‰,2SD),GSD-11(0.12±0.11‰,2SD),2711a(0.23±0.12‰,2SD)and GSS-5(0.32±0.11‰,2SD)is consistent with previous reports;water system sediment GSD-12 and soil GSS-6 are slightly different from previous reports,which may be related to sample batch and inhomogeneity.In addition,the Sb isotope composition of 16 standard samples such as basalt(BCR-2)is our first report,which will help enrich the data of antimony reservoirs in nature,facilitate horizontal comparison between laboratories,and jointly promote the antimony isotope system construction and development.(3)The Shadi weathering profile ranges from fresh shale(SD series),weakly weathered shale(SDI series)to strongly weathered shale(SDIII series).The minimum?^123/121Sb value in the sample is-0.57‰,the maximum is 0.10‰,and the maximum change is 0.67‰,and the average value is-0.37±0.08‰(2SD,n=16).The?^123/121Sb value of the strongly weathered samples in the upper part of the profile is greater than that of the fresh and weakly weathered samples in the middle part,and the Sb isotope has been significantly fractionated.And as the degree of weathering strengthened,the samples gradually enriched heavy Sb isotopes,which may be affected by redox changes,iron oxides,aluminum oxides adsorption and other factors.